Alloy for permanent magnets



NTUOC ALLOY FOR PERMANENT MAGNETS Clarence George Bieber, Huntington, W. Va., as-

UNITED STATES PATENT OFFICE Signor to The International Nickel Company,

Inc., New York, N. Y., a corporation of Delaware No Drawing. Application June 4, 1942,

Serial N 0. 445,809

' manent magnets and more particularly to alloys of the age hardening type which may be forged and hot rolled to small section sizes.

In my copending application, Serial No. 340,- 997, filed June 1'7, 1940, I have disclosed alloys suitable for use in making permanent magnets which combined good magnetic properties with hot forgeability. These alloys, however, were not sufficiently ductile to be rolled to thin sections; For example, it is not commercially feasible to hot roll the alloy to x A" flats which are required for certain types of magnets.

The word forgeability as used herein describes that property of an alloy which permits hot deformation of the cast material, 1. e., prior to the time that the cast structure has been broken up by working. The term rollability as used herein refers to that property of metals and alloys which permits deformation of the wrought structure, 1. e., the ability of the material to stand deformation after the cast structure has been broken up by working. In order to withstand rolling to thin sections of the order of inch or less, a material must be ductile or malleable, i. e., possess the ability to Withstand deformation, over a comparatively broad temperature range since the material tends to cool quite rapidly during the hot working operations.

I have now discovered that the temperature range of malleability of the alloys disclosed in the copending application referred to above can be significantly broadened by lowering the aluminum and nickel content. For example, an alloy containing about 28% nickel, 8% aluminum, and 2% titanium with the balance iron has a temperature range of hot malleability extending from about 250 F. down to 1900 F. An alloy containing nickel within the range of about 18 to 23%, aluminum, 2% titanium and the balance iron, has a hot ductile range extending from about 2500 F. to 1700 F., a range almost 50% broader than the alloy having higher nickel and aluminum. The magnetic properties of the alloy suffer, however, when the aluminum and nickel are lowered. The first alloy mentioned has a BHmax in the heat treated condition in excess of 1,500,000, whereas the BHmax of the low nickellow aluminum type in the heat treated condition is in the neighborhood of about 500,000. While this value is still high compared to known forgeable magnet steels except the very high cobalt types, it is not satisfactory for some applications where strong stable permanent magnets of small size or light weight are required.

The present invention is based upon the re cent discovery that the magnetic properties of the rollable alloys may be enhanced by the addition of cobalt,

It is an object of my invention to provide an age hardenable alloy, of the nickel-iron type having high residual magnetism and coercive force which may be hot rolled into shapes required for individual permanent magnets of thin section.

It is another object of my invention to provide permanent magnets made of hot rolled and age hardened nickel-iron alloy characterized by high coercive force .andhigh residual magnetism. Other objectsand; advantages of the present invention will becomeapparent from the following description of the-invention.

Generally speaking,. my novel alloy comprises as essential-ingredients nickel, iron, aluminum and titanium in controlled and critical amounts so correlated as to produce a rollable composition to which cobalt is added to enhance the residual magnetism and/ or coercive force. While the temperature range of hot malleability is narrowed somewhat by'cobalt in some cases, alloys can be produced in accordance with the present invention which have an improved combination of magnetic properties and hot rollability.

," The following specific examples are given to acquaint those skilled in the art with some of the advantages of the present invention:

Composition P Percent ercent Alloy No. increase 32 32 2 Al Ni Tl Co Fe able range 5 l8 2 10 B61. 17. 3 l2. 5 5 23 2 l0 Bal. 32 0 6 18 2 10 B111. 49. 2 0 6 23 2 10 Bal. 35. 7 l6. 7 7 l8 2 10 B51. 71. 5 l4. 3 7 23 2 l0 Bel. 64. 7 28. 6 8 23 2 10 B211. 36. 8 46. 3

In' the foregoing table the percent change in BHmax or in the temperature rang of hot malleability was determined by comparing the properties with alloys having the same amount of aluminum, nickel and titanium but which were substantially cobalt-free. It will be seen from th table that very significant improvement in magnetic properties, as evidenced by the BHmax, can be obtained by the addition of cobalt without greatly narrowing th temperature range of hot malleability, provided the aluminum content is less than about 8%. Cobalt tends to affect the forgeability of the alloys adversely and it may be necessary in certain cases to exercise some caution in forging the alloys until the cast structure has been broken up. After this has been accomplished, the alloys, in general, can be further hot worked, e. g., by rolling into relatively this sections from which small light-weight permanent magnets can b fabricated.

The broad composition ranges within which satisfactory alloys embodying the present invention may be made are as follows:

Percent Nickel 15-30 Aluminum 4-9.5 Titanium 1-3 Carbon -0.25 Cobalt 1-15 Iron Balance The foregoing ranges are critical. Thus, if

nickel exceeds 30%, the alloy is unforgeabl even in the absence of cobalt. Similarly, if aluminum exceeds 9.5% or titanium exceeds 3%, the alloy breaks up when an attempt is made to forge it. Moreover, with high nickel, the cobalt content cannot also be in the upper part of the cobalt range. For example, an alloy containing 28% nickel, 8% aluminum, 2% titanium and the balance iron forged satisfactorily but become unforgeable with the addition of 10% cobalt.

The presence of carbon, e. g., in an amount approximating 0.1%, aids the forgeability of alloys containing nickel in the upper part of th range and in some cases where forgeability presents a serious problem, it may be advisable to employ carbon even up to about 0.25%. The magnetic properties, however, are somewhat adversely affected by carbon and it is preferred therefore not to have more carbon present than is required for satisfactory forgeability and where satisfactory forgeability may be had without carbon, the carbon is maintained as low as practicable and may even be entirely absent.

In order to obtain the optimum combination of magnetic propertie and rollabllity, the alloys ordinarily will be made within the following preferred ranges:

Percent Nickel 24-27 Aluminum 6-8 Titanium 2 Cobalt -10 Iron Balance Within this composition range, rollable alloys having a BHmax approximating and in some cases exceeding 1,000,000 may be obtained which can be produced in complicated sections, e. g., sections of about inch thickness which are suitable for manufacturing stable light-weight permanent magnets.

The alloy may be made in any suitable way, e. g., as disclosed in the copending application referred to above, except that cobalt is included in the initial charge. The alloys of the present invention may also be heat treated as disclosed in said copending application or by any other suitable process.

The elements boron, lead, arsenic, antimony, bismuth, sulphur, selenium and tellurium are detrimental to the hot malleability of the alloys of the present invention and should not exceed about 0.05%. Silver, tin and phosphorus likewise are detrimental to the hot malleability of the alloy and should be kept below about 0.1%. Calcium, strontium and barium are somewhat benefinial to the hot malleability when present in con centrations of the order of about 0.01 to 0.02%

but become detrimental to the hot malleability when they exceed about 0.1%. Copper, vanadium, columbium, tantalum, chromium, molybdenum and tungsten have been found to be detrimental to the hot malleability of the alloy when present in amounts exceeding about 1% and are preferably maintained below this level. Managanese may be present up to about 1% without detrimentally affecting magnetic or working properties.

In the specification and claims the term balance iron signifies that iron is the predominating constituent of the alloy but that it may contain impurities or other alloying elements in small amounts as set forth hereinabove.

The present invention is in the nature of a continuation in part of my prior copending application, Serial No. 340,997, filed June 17, 1940, Patent No. 2,285,406, granted June 9, 1942.

Although the present invention has been described with reference to particular compositions, certain modifications and variations in the composition and/or method of making the permanent magnets may be made as those skilled in the art will readily appreciate. Thus, for example, zirconium may be substitu for the titanium.

I claim:

1. An alloy comprising about 24% to 27% nickel, 5% to 10% cobalt, 6% to 8% aluminum, 2% titanium, and the balance iron.

2. An alloy comprising about 15% to 30% nickel, 1% to 15% cobalt, 4% to 9.5% aluminum, 1% to 3% titanium, and the balance iron and minor constituents of which carbon does not exceed 0.25%. I 3. A hot rollable alloy having properties adapting it for us as a permanent magnet comprising about 15% to 30% nickel, 1% to 15% cobalt, the cobalt and nickel being so related that the cobalt content does not fall in the upper part of the cobalt range when nickel is in the upper part of the nickel range, 4% to 9.5% aluminum, 1% to 3% titanium, less than 0.25% carbon and the balance iron.

4. A permanent magnet made of hot worked alloy comprising about 24% to 27% nickel, 5% to 10% cobalt, 6% to 8% aluminum, 2% titanium, and the balance iron.

5. A permanent magnet made of hot worked alloy comprising about 15% to 30% nickel, 1% to 15% cobalt, 4% to 9.5% aluminum, 1% to 3%, titanium, and the balance iron and minor constituents, of which carbon does not exceed about 0.25%.

CLARENCE GEORGE BIEBER.

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